2006_A New Algorithm for Distorted Fingerprints Matching Based on Normalized Fuzzy Similarity Measure

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    768 IEEE TRANSACTIONS ON IMAGE PROCESSING, VOL. 15, NO. 3, MARCH 2006

    line. Kovacs-Vajna et al. [17] also proposed a method based

    on triangular matching to cope with the strong deformation

    offingerprint images, demonstrating graphically that the large

    cumulative effects can be a result from the small local distor-

    tions. Bazen et al. [18] employed a thin-plate spline model

    to describe the nonlinear distortions between the two sets of

    possible matching minutiae pairs. By normalizing the inputfingerprint with respect to the template, this method is able to

    perform a very tight minutiae matching.

    Different from the above mentioned methods, we propose an

    algorithm based on fuzzy theory to deal with the nonlinear dis-

    tortion in fingerprint images. First, an algorithm was defined to

    deal with the spurious minutiae. Then the algorithm aligns the

    template and inputfingerprints using the registration method de-

    scribedbyLuo etal.[19],andlocaltopologicalstructurematching

    wasintroducedto improve the robustnessof global alignment.Fi-

    nallya novel similaritycomputingmethod based on fuzzytheory,

    NFSM,wasconductedtocomputethesimilaritybetweenthetem-

    plateandinput fingerprints. Experimental results indicate thatthe

    proposedalgorithmworkswellwiththenonlineardistortions.Fordeformed fingerprints, the algorithm gives considerably higher

    matching scores compared to conventionalmatching methods. In

    fingerprints database DB1 and DB3 of FVC2004, the distortion

    between some fingerprints from the same finger is large, but our

    algorithm performs well. The equal error rates (EER) are 4.37%

    and 1.64% on DB1 and DB3, respectively.

    This paper is organized as follows. Section II indicates out the

    fingerprint feature representation and extraction. A method is

    defined to deal with the spurious minutiae. Section III describes

    the local topological structure matching. Section IV proposes

    the novel method, NFSM, which is applied to compute the sim-

    ilarity between the template and input fingerprints. The perfor-mance of the proposed algorithm is shown by experiments in

    Section V. Section VI presents our conclusion and discussion.

    II. FEATURE REPRESENTATION AND EXTRACTION

    For an input fingerprint image, the method described by

    Hong et al. [20] is used to enhance the image, and the thinned

    ridge map is obtained. The thinned ridge map is postpro-

    cessed by using Luos method [21]. Then the minutiae set

    is detected by using Hongs method [20]. For each belongs

    to , the associate ridges or valleys in are traced and some

    sample points with constant intervals are recorded. The

    minutiae set and the sample points on the associate ridges and

    valleys provide information for both alignment and discrimina-

    tion. An example of the feature set of a live-scan fingerprint is

    provided in Fig. 1.

    A critical and difficult step in fingerprint matching is to re-

    liably extract minutiae from the input fingerprint images. The

    performance of a minutiae extraction algorithm highly relies on

    the quality of the input fingerprint images. In an idealfingerprint

    image, ridges and valleys alternate and flow in a local constant

    direction and minutiae are anomalies of ridges, i.e., ridge end-

    ings and ridge bifurcations. In such situations, the ridges can be

    easily detected and minutiae can be precisely located from the

    thinned ridges. However, in reality, approximately 10% [20] ofacquired fingerprint images are of poor quality due to variations

    Fig. 1. Feature set of a live-scan fingerprint image. (a) Original fingerprintimage. (b) Thinned ridge image with minutiae and sample points of (a).

    in impression conditions, ridge configuration, skin conditions,

    acquisition devices, and noncooperative attitude of subjects, etc.

    The ridge structuresin poor-qualityfingerprintimages arenot al-

    ways well-defined and, therefore, cannot be correctly detected.

    A significant number of spurious minutiae may be created as aresult. In order to ensure that the performance of the minutiae

    extraction algorithm will be robust with respect to the quality of

    input fingerprint images, an enhancement algorithm which can

    improve the clarity of the ridge structures is necessary. However,

    forpoorfingerprint image, somespuriousminutiae may stillexist

    afterfingerprint enhancement and postprocessing.It is necessary

    to propose a method to deal with the spurious minutiae.

    A method to judge whether an extracted minutia is a true one

    has been proposed in this paper. According to our work, the dis-

    tance between true minutiae is generally greater than threshold

    (thre). While near the spurious minutiae, there are usually other

    spurious minutiae. On the other hand, spurious minutiae are usu-

    ally detected at the border of fingerprint image. Examples of

    spurious minutiae in poor quality fingerprint images are shown

    in Fig. 2.

    The following algorithm is performed to detect the spurious

    minutiae. In this process, a few true minutiae may be considered

    as spurious ones, but this does not affect further match process.

    Step 1: Judge whether the minutia is close

    to the border of the fingerprint image.

    The fingerprint mask is obtained by using

    Hongs algorithm [20]. The distance disMB

    between the minutiae and the fingerprint

    border is computed. If (ac-

    cording to our work, ), then it is

    considered as spurious minutia, else goto

    step 2.

    Step 2: Search minutiae center around the

    minutia Mi within thre radius, obtain the

    number of minutiae num.

    Step 3: If (according to our

    work, ), then it is considered as

    spurious minutia, otherwise as a true one.

    It is an efficient and simple method to detect the spurious

    minutiae. None of the detected spurious minutiae are partici-pated in the further match process.

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    Fig. 2. Examples of spurious minutiae in poor quality fingerprint images. Theimageshave been cropped and scaledfor view. (a) Original image.(b) Enhancedimage of (a), (c) original image, (d) enhanced image of (c). Many spuriousminutiae were detected in the process of minutiae extraction. Near the spuriousminutiae, there are usually other spurious minutiae as indicated in ellipses, andspurious minutiae are usually detected at the border of fingerprint image asshown in rectangles.

    III. MATCHING USING LOCAL TOPOLOGICAL STRUCTURE

    The proposed matching algorithm has two steps. First, Luos

    matchingmethod[19]whichmodifiedfromJainetal.salgorithm[22] has been used to process the coarse match. A changeable

    bounding box is applied during the matching process which

    makes it more robust to nonlinear deformations between the

    fingerprint images. Fig. 3 shows the illustrative diagram for

    changeable sized bounding box. The value of angle_size and

    radius_size of the bounding box in every minutia is changed

    according to the radius of the minutia. If the radius of the

    template minutia is larger, then its bounding box will have a

    larger radius_size and a smaller angle_size. We suppose an

    approximate alignment has already beenestablished at thisstage.

    If the approximate alignment is wrong, the further matching

    steps cannot recover this error. Then, local topological structure

    match is introduced to improve the robustness of match.

    A. Defining of Local Topological Structure

    Let denote a minutia in the fingerprint image and

    are the minutiae circled around within

    radius. Feature vector is used to describe

    the relationship between and denotes the distance

    between and denotes the angle between the orien-

    tation of minutia and the direction from to

    denotes the angle between the orientation of minutia

    and the direction from to . It is easy to see that the local

    topological structure feature vector isindependent from the rotation and translation of the fingerprint.

    Fig. 3. Illustrative diagram for changeable sized bounding box.

    Fig. 4. Local topological structure of P .

    Fig. 4 shows the meaning of each parameter. The local topo-

    logical structure of is defined as the following:

    B. Local Topological Structure Matching

    Suppose is a minutia in the template fingerprint,

    are minutiae circled around within radius.

    Then, the local topological structure of can be obtained as

    Suppose is a minutia in the input fingerprint and the input

    fingerprint is deformed. For the deformed input fingerprint,

    minutiae are searched in a circle around within

    radius. is the distance tolerance. Suppose are

    minutiae circled around within radius. Then, the local

    topological structure of can be expressed as

    The following algorithm is used to determine whether twominu-

    tiae and are matched.

    Step 1: For and , matched each

    entry , in the local topological struc-ture and each entry , in

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    770 IEEE TRANSACTIONS ON IMAGE PROCESSING, VOL. 15, NO. 3, MARCH 2006

    Fig. 5. Illustrative diagram for matching P Q ( l e n ; ; ) , andR S ( l e n ; ; )

    . (a) Topological structure ofP Q

    andR S

    .

    (b) The adaptive matching bounding box.

    the local topological structure , obtained the matched

    number of and .

    Three parameters , , are calculated as the

    following:

    (1)

    (2)

    (3)

    An adaptive matching bounding box is

    used to determine whether and is matched. The size

    of matching box changes according to the distance as

    seen in (4) and (5), shown at the bottom of the page, where

    , . The purpose for using a change-

    able sized bounding box is to deal with nonlinear deformation

    more robustly. Fig. 5 shows the illustrative diagram for matching

    , and .

    When the distance of is small, a small deformation will

    mean a large change of the radial angle while the change ofradius remains small. In this case the of the bounding box

    should be larger and the of the bounding box should be

    smaller. On the other hand, when the distance of is large,

    a small change in radial angle will cause a large change in the

    position of the minutia. The radius can have larger deformation

    as the accumulation of deformation from all the regions between

    and [17]. In this case, the of the bounding box

    should be larger and the should be smaller.

    If (1)(3) satisfy the following conditions:

    (6)

    (7)

    (8)

    then and are considered as matched.

    Step 2: If then goto Step 3, else and

    are considered as not matched.

    Fig. 6. Two cases of the local topological structure of P and R satisfy therequirement of step2. (a) Minutia

    P

    is actually not matched with minutiaR

    .(b) Minutia

    P

    is matched with minutiaR

    .

    Step 3: Fig. 6 shows two cases that the local topological

    structure of and satisfy the requirement of step2. In case

    (a), there are three minutiae , , circled around

    within radius and radius, but there are six minutiae

    circled around with radius. Although

    , minutia is actually not matched with

    minutia . In case (b), there are three minutiae , , cir-

    cled around within radius but six minutiae

    circled around within radius, and there are sixminutiae circled around with radius.

    As the fingerprint is deformed, minutia is considered as

    matched with minutia .

    Therefore, we need to handle the above two cases. We ob-

    tained another two local topological structure of

    and . is obtained by searching

    minutiae circled around within radius. Suppose these minu-

    tiae are . Then the local topological structure of

    can be expressed as

    is obtained by searching minutiae circled

    around within radius. Suppose these minutiae

    are . Then, the local topolog-

    ical structure of can be expressed as

    Then, using the algorithm described in step 1), match the local

    topological structure and , obtain the

    matched number .

    Step 4: If , then is matched with ,

    else not matched.

    Experiments were performed to evaluate the contribution of

    the proposed local topological structure match algorithm on

    if

    if

    otherwise(4)

    if

    ifotherwise. (5)

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    TABLE ICOMPARISON OF THE ALGORITHM WITH AND WITHOUT THE PROPOSED

    LOCAL TOPOLOGICAL STRUCTURE MATCH ON FVC2002 DB

    FVC2002 DB. Table I illustrates the comparison of the algo-

    rithm with and without the proposed local topological structure

    match on FVC2002 DB. It is clear that the proposed local

    topological structure match algorithm has obviously improved

    the overall performance.

    IV. NORMALIZED FUZZY SIMILARITY MEASURE

    Computing the similarity between deformed template and

    input fingerprints is a difficult task. In some algorithms [3], [18],

    the number of matching minutiae was only used to compute

    the similarity between template and input fingerprints. Most

    algorithms increase the size of the bounding boxes in order to

    tolerate the further apart of matched minutiae pairs because ofplastic distortions and, therefore, to decrease the false rejection

    rate (FRR). However, as a side effect, this method may lead

    higher false acceptance rate (FAR) by making nonmatching

    minutiae get paired. Different from the above mentioned algo-

    rithm, we proposed a novel similarity computing method based

    on fuzzy theory to calculate the similarity between template

    and input fingerprints images.

    A. Feature Representation of Similarity Measure

    Two features are selected: the number of matched sample

    points (n) and the mean distance difference of the matched minu-

    tiae pairs (d) in the process of similarity computing . Using the

    proposed algorithm defined in Section III, the matched minutiae

    pairs between template and input fingerprints can be obtained.

    The corresponding sample points are considered to match if

    their associated minutiae are matched. If the number of sample

    points for one minutia in a pair is different from the second

    minutia of the pair, we set the smaller number as the number of

    matched sample points. Suppose there are matched minutiae

    pairs, and there are matched sample points for every minutiae

    pair, then the sum of matched sample points is calculated as

    follows:

    (9)

    Fig. 7. Probability distribution ofn

    in Genuine match and Imposter match onFVC2002 DB1.

    Fig. 8. Probability distribution ofd

    in Genuine match and Imposter match onFVC2002 DB1.

    and the mean of distance difference between every two minutiae

    is calculated as follows:

    (10)

    Where the meaning of can be seen in expression (1).

    Experiments were performed to characterize the features:

    and . The experiments were done on FVC2002 DB1. It con-

    tains 800 fingerprint images captured by optical sensor Identix

    TouchView II. According to FVC rules [1], each sample ismatched against the remaining samples of the same finger in

    genuine match. Hence, the total number of genuine tests (in case

    no enrollment rejections occur) is: .

    In imposter match, the first sample of each finger is matched

    against thefirst sample of the remainingfingers. Hence, the total

    number of false acceptance tests (in case no enrollment rejec-

    tions occur) is: . All of n and d samples

    from genuine match and imposter match were used to construct

    fuzzy feature sets and , respectively. Figs. 7 and 8 show

    the probability distribution of n and d in genuine match and im-

    poster match on FVC2002 DB1. From Figs. 7 and 8, wefind that

    has excellent classification performance and the classification

    performance of d is also good. Fig. 9 shows a scatter plot of dagainst n for all examples in genuine match and imposter match

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    Fig. 9. Scatter plot of d against n for all examples on FVC2002 DB1.

    on FVC2002 DB1. The fuzzy feature sets and are clus-

    tered into two classes. One is corresponding to genuine match

    samples and the other is to imposter match samples.

    B. NFSM Measure

    Fuzzy features were used to represent and . Each character

    is associated with a fuzzy feature that assigns a value (between

    0 and 1) to each feature vector in the feature space. The value,

    named degree of membership, illustrates the degree of similarity

    of the template and input fingerprints.

    A fuzzy feature on the feature space is defined by a

    mapping named as the membership function.

    For any feature vector , the value of is called the

    degree of membership of to the fuzzy feature . The value ofis more close to 1, the input fingerprint is more similar

    to the template one. For the fuzzy feature , there is a smooth

    transition for the degree of membership to besides the hard

    cases and . It is clear

    that a fuzzy feature degenerates to a conventional feature set if

    the range of is instead of .

    Building or choosing a proper membership function is an ap-

    plication dependent issue. Some most commonly used prototype

    membership functions are cone, exponential, and Cauchy func-

    tions [23]. In the proposed algorithm, the Cauchy function is

    chosen due to its good expressiveness and high-computational

    efficiency [24].

    The Cauchy function: , is defined as

    (11)

    where , and , , . is the center

    location of the fuzzy set, represents the width ( for

    ) of the function, and determines the smoothness

    of the function. Generally, and portray the grade of fuzzi-

    ness of the corresponding fuzzy feature. For fixed , the grade

    of fuzziness increases as decreases. For fixed , the grade offuzziness increases as increases.

    Accordingly, feature is represented by fuzzy feature

    whose membership function, , is defined as

    (12)

    where represents the distance between

    and and are the genuine and imposter match clusters

    center of fuzzy set .

    Feature is represented by fuzzy feature whose member-

    ship function, , is defined as

    (13)

    where represents the distance between

    and and are the genuine and imposter match clusters

    center of fuzzy set .An intrinsic property of membership function (12) and

    (13) is that the farther a feature vector moves away from the

    cluster center, the lower the degree of membership is to the

    fuzzy feature. At the same time, the degrees of membership

    to the other fuzzy features may be increasing. This clearly

    describes the gradual transition of two clusters. Table II shows

    the respective classification performance of and

    on FVC2002 DB.

    In order to achieve the better classification performance,

    and are combined. The detailed analysis on

    combining classifiers can be seen in the literatures [25][27].

    After combination, the similarity is needed to normalize to

    . Four rules were used to combine and . In

    these four rules, the similarity is always in the real interval

    because and are always within .

    1) Max rule:

    (14)

    2) Min rule:

    (15)

    3) Product rule:

    (16)

    4) Mean rule:

    (17)

    Experiments were performed to evaluate four similarity com-

    puting rules on FVC2002 DB. Table II shows the comparison

    of performance on FVC2002 DB in different similarity com-

    puting rules. On DB1, if only is used to classify in fin-

    gerprint matching, EER is 3.03%, and if only is used to

    classify in fingerprint matching, EER is 20.13%. While using

    the product rule to compute the similarity, EER is decreased to0.19%. From Table II, we can clearly tell that the performance

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    TABLE IICOMPARISON OF PERFORMANCE ON FVC2002 DB

    IN DIFFERENT SIMILARITY COMPUTING RULES

    Fig. 10. Experimental results of the proposed algorithm on FVC2002 DB1.

    of product rule is the best while the performance of max rule is

    the worst. Hence, the product rule was selected in the proposed

    algorithm to compute the similarity between the template and

    input fingerprints. Fig. 10 shows the experimental results of the

    proposed algorithm on FVC2002 DB1.

    V. EXPERIMENTAL RESULTS

    The proposed algorithm has been participated in

    FVC2004. In FVC2004, databases are more difficult than in

    FVC2000/FVC2002 ones. In FVC2004, the organizers have

    particularly insisted on: distortion, dry, and wet fingerprints.

    Especially in fingerprints database DB1 and DB3 of FVC2004,the distortion between some fingerprints from the same finger is

    Fig. 11. Example of large distortion from FVC2004 DB1. (a) 102_3.tif;(b) 102_5.tif; (c) image which (a) (after registration) was added to (b). In therectangle region, the corresponding minutiae are approximately overlapped.While in the ellipse region, the maximal vertical difference of correspondingminutiae is above 100 pixels.

    large. Our work is to solve the problem of distorted fingerprintmatching, so the evaluation of the proposed algorithm is

    mainly focused on DB1 and DB3 of FVC2004. The proposed

    algorithm is also compared with the one described by Luo et

    al. [19] and the one proposed by Bazen et al. [18].

    A. Performance On FVC2004 DB1

    The fingerprints of FVC2004 DB1 were acquired through

    CrossMatch V300 (Optical sensor). The size of the image is

    640 480 pixels with the resolution about 500 dpi. The fin-

    gerprint database set A contains 800 fingerprint images cap-

    tured from 100 different fingers, eight images for each finger.

    Fig. 11 shows an example of large distortion from FVC2004DB1 (102_3.tif and 102_5.tif). While the corresponding minu-

    tiae in green region are approximately overlapped, the maximal

    vertical difference of corresponding minutiae in red region is

    above 100 pixels. Fig. 12 indicates our enhanced and matched

    results on 102_3.tif and 102_5.tif. Using the proposed algo-

    rithm, the similarity between these twofingerprints is 0.420 082.

    Fig. 13 presents another fingerprint pair with large distortion

    from FVC2004 DB1. The similarity between these two finger-

    prints is 0.650 000. The performance of the proposed algorithm

    on FVC2004 DB1 is shown in Fig. 14, and from which we find

    that the similarity threshold at EER point is about 0.28, so we

    judge that the above two fingerprint pairs come from the same

    finger. The two matches are successful. The EER of the pro-posed algorithm on FVC2004 DB1 is about 4.37%. The average

    time for matching two minutiae sets is about 0.77 s on PC AMD

    Athlon (1.41 GHz).

    B. Performance On FVC2004 DB3

    The fingerprints of FVC2004 DB3 were acquired through

    thermal sweeping sensor FingerChip FCD4B14CB by Atmel.

    The size of the image is 300 480 pixels with the resolution

    of 512 dpi. In this fingerprints database, the distortion between

    some fingerprints from the same finger is large. Fig. 15 shows a

    fingerprint pair with large distortion from FVC2004 DB3. Using

    the proposed algorithm, the similarity between these twofinger-prints is 0.484 111. The performance of the proposed algorithm

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    Fig. 12. Experimental results of the proposed algorithm on 102_3.tif and

    102_5.tif in FVC2004 DB1. The images have been cropped and scaled forview. (a) 102_3.tif. (b) Enhanced image of 102_3. (c)102_5.tif. (d) Enhancedimage of 102_5. The similarity of these two fingerprints is 0.420 082.

    Fig. 13. Experimental results of the proposed algorithm on 109_3.tif and

    109_4.tif in FVC2004 DB1. The images have been cropped and scaled forview. (a) 109_3.tif. (b) Enhanced image of 109_3. (c) 109_4.tif. (d) Enhancedimage of 109_4. The similarity of these two fingerprints is 0.650 000.

    on FVC2004 DB3 is shown in Fig. 16. It indicates that the sim-

    ilarity threshold at EER point is about 0.26, so we can judge

    that the fingerprint pair comes from the same finger. The EER

    of our algorithm on FVC2004 DB3 is about 1.64%. The average

    time for matching two minutiae sets is about 0.81 s on PC AMDAthlon (1.41 GHz).

    Fig. 14. Experimental results of the proposed algorithm on FVC2004DB1_A.The fingerprint images were acquired through optical sensor.

    Fig. 15. Experimental results of the proposed algorithm on 103_2.tifand 103_4.tif in FVC2004 DB3. The images have been scaled for view.(a) 103_2.tif. (b) Enhanced image of 103_2. (c) 103_4.tif. (d) Enhanced imageof 103_4. The similarity of these two fingerprints is 0.484 111.

    Fig. 16. Experimental results of the proposed algorithm on FVC2004DB3_A.The fingerprint images were acquired through thermal sweeping sensor.

    The proposed algorithm has good performance on finger-

    prints database DB2 and DB4 of FVC2004 as well. EER are

    2.59% and 0.61%, respectively. The processing time is 0.58and 0.56 s, respectively.

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    TABLE IIICOMPARISON OF MATCHING SCORE IN THE NFSM

    ALGORITHM TO LUOS METHOD

    Fig. 17. Example of false acceptance on a pair of fingerprints capturedfrom CrossMatch sensor. The images have been cropped and scaled for view.(a) Original image. (b) Enhanced image of (a). (c) Original image. (d) Enhanced

    image of (c). The fingerprint pair is very similar, but they are from differentfinger. The similarity of the two fingerprints is 0.431 516.

    C. Comparison of NFSM With Other Algorithm

    The proposed algorithm is compared with the one described

    by Luo et al. [19]. The Comparison is performed on FVC2004

    DB1. In Luos method, a changeable bounding box was used

    during the matching process. It is more robust to nonlinear de-

    formations between the fingerprint images. However, the dis-

    tortion among some fingerprints from the same finger captured

    from the CrossMatch sensor is too large. In order to tolerate

    matching minutiae pairs that are further apart because of distor-

    tions, the size of the bounding boxes has to be increased. How-

    ever, as a side effect, it gives a higher probability for those non-

    matching minutiae pairs to get paired, resulting in a higher falseacceptance rate. Table III lists the comparison of matching score

    of the proposed algorithm to Luos method. It is clear that case

    1 and case 2 have been successfully matched in our NFSM al-

    gorithm. While for Luos method, when size of the bounding

    boxes is 15, case 1 and case 2 are false rejected, and when size

    of the bounding boxes is increased to 25, case 2 is accepted but

    case 1 is false rejected, meanwhile EER is increased from 9.13%

    to 9.92%. Moreover, EER of the proposed algorithm is 4.37%,which is much lower than Luos method of 9.13%.

    The proposed algorithm is also compared with Bazens

    method [18]. In their training database of FVC2002 DB1, for

    Bazens algorithm, the EER of the ROC turned out to be 1.8%

    with for elastic matching. While in our algorithm, the

    EER on FVC2002 DB1 is only about 0.19%. The experimental

    results of our algorithm on FVC2002 DB1 are shown in Fig. 10.

    The results conform that the performance of the proposed algo-

    rithm surpasses Bazens algorithm.

    VI. CONCLUSION AND DISCUSSION

    Coping with nonlinear distortions in the matching algorithmis a challenging task. In this paper, we proposed a novel algo-

    rithm to deal with the nonlinear distortion in fingerprint images.

    A novel similarity computing method based on fuzzy theory,

    NFSM, is introduced to compute the similarity between the tem-

    plate and input fingerprints. Experimental results show that the

    algorithm gives considerably higher matching scores compared

    to conventional matching algorithms for deformed fingerprints.

    Our algorithm has been participated in FVC2004. The Partici-

    pant ID is P071 (open). The detailed performance of the pro-

    posed algorithm on FVC2004 can be seen from the website

    http://bias.csr.unibo.it/fvc2004/default.asp. In fingerprints data-

    base DB1 and DB3 of FVC2004, the distortion between some

    fingerprints from the same finger is large. However, EER areonly 4.37% and 1.64% on DB1 and DB3, respectively, in our

    algorithm, and it performs well on processing time, the average

    time for matching two minutiae sets is about 0.67 s.

    However, there are still few false acceptances in fingerprint

    matching process. Fig. 17 shows an example of false acceptance

    on a pair offingerprints captured from CrossMatch sensor. The

    pair is very similar, but they are from different finger. Further

    investigation is going on to advance the algorithm for its false

    acceptance which occasionally happens.

    REFERENCES

    [1] Biometric Systems Lab., Pattern Recognition and ImageProcessing Lab. Biometric Test Center. [Online]. Available:http://bias.csr.unibo.it/fvc2004/

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    Xinjian Chen received theB.S. degreein geophysicsfrom Centre South University of Technology, China,in 2001. He is currently pursuing the Ph.D. degreeat the Institute of Automation, Chinese Academy ofSciences, Beijing.

    His research interests include pattern recognition,machine learning, image processing, and their appli-cations in biometrics.

    Jie Tian (SM02) received the Ph.D. degree (with

    honors) in artificial intelligence from the Institute ofAutomation, Chinese Academy of Sciences, Beijing,in 1992.

    From 1994 to 1996, he was a Postdoctoral Fellow

    with the medical image processing group, Universityof Pennsylvania, Philadelphia. Since 1997, he hasbeen a Professor with the Institute of Automation,Chinese Academy of Sciences. His research interestsinclude pattern recognition, machine learning, imageprocessing and their applications in biometrics, etc.

    Xin Yang received the Ph.D. degree in precision in-struments from TianJing University, China, in 2000.

    She is a Postdoctoral Fellow with Institute ofAutomation, Chinese Academy of Sciences, Beijing.Her research interests include pattern recognition

    and its applications in biometrics.